Redirecting all sites (not desired) to the same URL

We have a online service where we set up each client with a seperate system. To access the site, they go to their specific URL, ie, companyname.product.biz. We are migrating the sites to a new server (a few at a time) and are redirecting the sites to the new location as we go. The new sites are companyname.product.com. Last night during our moves, a change was made so that ALL sites not currently redirected (it did not affect the 40 redirects already in place) were redirected to the same .com site. Our developer who is handling the technical side has fixed this, but has not provided a good explaination as to how this happened and I've got a few clients asking. I've got limited knowledge of IIS but will try to answer any questions to help identify the cause of this. Not that it matters (at least I don't think so), but the underlying application is a SQL database service.